This invention relates to compressed digital multi-channel video communications system, and more particularly to such a system which is provided with one or more auxiliary channels that allow an increase in the instantaneous effective bit rate for any of the assigned signal-carrying channels.
Considerable work is underway in connection with the development of digital multi-channel video communications systems, such as cable and direct broadcast satellite systems, in which conventional analog video signals are replaced by digital bit streams. Typically, the data transmitted in each channel is compressed, successive video frames being coded according to the MPEG1 or MPEG2 standards. Compression techniques are designed to allow the transmission of sufficient information to represent full motion video in a standard bandwidth channel. (As used herein, the term "channel" is broad and includes not only the channel of a cable or direct broadcast satellite system, but also a channel recording, e.g., on an optical disk.)
Unfortunately, it has been discovered that the digital compression schemes that have been proposed do not always allow the representation of full motion video. This is especially true for fast-changing scenes, for example, a fast-moving football. Even if the encoding bit rate of a channel is variable, there is an instantaneous upper limit and there are necessarily times when the digitally-derived picture is of poorer quality than the conventional analog picture.
It is therefore an object of my invention to provide a communications system for which there is less degradation in fast-changing scenes.